GSLIB Help Page: SASIM

Description:

sasim allows conditional simulations of a continuous variable
honoring any combination of the following input statistics: histogram,
variogram, indicator variograms, correlation coefficient with a
secondary variable, or conditional distributions with a secondary
variable.

Parameters:

objhist, objvarg, objivar, objcorr, objcpdf: binary flags that
specify whether or not a component objective function will be
considered (set to 1 if yes, 0 if not).

sclhist, sclvarg, sclivar, sclcorr, sclcpdf: user imposed scaling
factors that will multiply the scaling factors that the program
automatically calculates (see section V.6).

ilog: if set to 1, the logarithm (base 10) of the variable will
be considered. This is appropriate for positively skewed variables
with large variance.

nsim: the number of realizations to generate.

nx, xmn, xsiz: definition of the grid system (x axis).

ny, ymn, ysiz: definition of the grid system (y axis).

nz, zmn, zsiz: definition of the grid system (z axis).

seed: random number seed (a large odd integer).

idbg: an integer debugging level between 0 and 3.

dbgfl: the file for the debugging output.

outfl: the output grid is written to this file. The output
file will contain the results, cycling fastest on x then y
then
z then simulation by simulation.

isas: the annealing schedule (next set of parameters) can be set
explicitly or it can be set automatically (0=automatic,1=then use the
next three lines of input).

t0, redfac, ka, k, num, omin: the annealing schedule: initial
temperature, the reduction factor, the maximum number of perturbations
at any one given temperature, and the target number of acceptable
perturbations at a given temperature, the stopping number (maximum
number of times that the ka is reached), and a low objective
function value indicating convergence.

maxpert: the maximum number of perturbations (will be scaled by
nx x ny x nz)

report: After a fixed number of swaps (report scaled by
nx x ny x nz) the objective function is
written to the screen and the debugging file.

icond: set to 1 if there is conditioning data (0 implies no
conditioning data).

condfl: an input data file with the conditioning data
(simplified GeoEAS format). If this
file does not exist then an unconditional simulation is
generated.

icolx, icoly, icolz, and icolvr: the column numbers for
the x,y, and z coordinates and the variable to be
simulated. One or two of the coordinate column numbers can be set to
zero which indicates that the simulation is 2D or 1D.

tmin and tmax: all values strictly less than tmin
and strictly greater than tmax are ignored.

ihist: set to 1 if the histogram should be taken from the
following file (set to 0 if not).

histfl: an input data file with the histogram in simplified
GeoEAS format.

icolvr, and icolwt: the column numbers for
the variable to be simulated and a declustering weight.

nquant: number of quantiles for the histogram objective function

nivar: number of indicator variograms to consider. The threshold
values (in units of the primary variable) are input next and the
variograms are input directly after the direct variogram of the primary
variable with the same format.

ithreshold: The threshold values (in units of the primary
variable) for the indicator variograms

secfl: an input data file with the secondary variable model
(needed if cosimulation is being performed)

icolsec: the column number for the secondary variable in
secfl

vertavg: if set to 1, then the correlation applies to the
secondary variable and a vertical average of the variable being
simulated. Otherwise, the secondary variable is considered at each
grid node location.

corrcoef: The correlation coefficient (used if the fourth
component objective function is turned on).

bivfl: an input data file with the bivariate data to define the
conditional distributions (simplified GeoEAS format)

icolpri and icolsec: the column numbers for
the primary and secondary variables in bivfl

tmin and tmax: all values strictly less than tmin
and strictly greater than tmax are ignored.

npricut: number of thresholds to define the conditional
distributions of the primary variable within a class of the secondary
variable.

nseccut: number of thresholds to define the classes of
secondary variable.

nlag: the number of variogram lags to consider in the objective
function. The closest nlag lags, measured in terms of
variogram distance, are retained.

istand: a flag specifying whether or not to standardize the sill
of the semivariogram to the variance of the univariate distribution
(istand=1 will standardize).
It is essential that the variance of the values of the
initial random image matches the spatial (dispersion) variance implied
by the variogram model. That dispersion variance should be equal to the
total sill if it exists (i.e., a power model has not been used) and
the size of the field is much larger than the largest range in the
variogram model.

nst and c0: the number of variogram structures and the
isotropic nugget constant

For each of the nst nested structures one must define it,
the type of structure; cc, the c parameter;
ang1,ang2,ang3, the angles defining the geometric anisotropy;
aa_hmax, the maximum horizontal range; aa_hmin,
the minimum horizontal range; and aa_vert, the vertical
range. A detailed description of these parameters is given in
section II.3.

Indicator variograms follow the definition of the direct primary
variable variogram.